Official figures sent out for campaigning purposes to Tory activists in constituencies throughout England and Wales appeared to show that there had been sharp increases in violence during Labour's time in office.

But a BBC investigation found that the Conservatives omitted Home Office warnings that the figures for the periods before and after 2002 were not comparable because of a change in the way violent crime was recorded.

Instead of police officers deciding whether an incident should be recorded as a violent crime, the decision was given to the alleged victim, with the effect of forcing up recorded violence by an estimated 35% in the first year, according to the BBC.

The British Crime Survey suggested that people's experience of violent crime has in fact fallen by around 50% since 1995.

Chris Grayling, the shadow home secretary, defended using the statistics without any warning to alert readers to the change in recording methods.

He told BBC Radio 4's Today programme this morning: "There are certainly changes in the recording methods, but the point is that they are the only comparators available. They are published by the Home Office.

"We don't create crime figures. We use the official crime figures published by the Home Office. The Home Office has continued to use the same comparators. As an opposition party, we don't make the statistics. We can only use what the Home Office publishes."

Grayling said that the British Crime Survey was not a reliable guide to violent crime because it omitted offences such as murder and manslaughter.

He said that an independent assessment of the Home Office's use of statistics in 2006 found that warnings attached to official figures were designed to be politically advantageous to the government.

"If you talk to anybody in the streets, and particularly in the poorest areas which are most affected by violent crime, you will find people will absolutely say that violent crime has risen sharply over the last 10 years," he said.

"The reality is that that is the life they are experiencing. The problem we have got to deal with is not debates over statistics. It is actually sorting out these problems, it is delivering better policing in these areas and getting to grips with the problems in these communities."